While the manufacture of polyolefin based fiber, webs and corresponding nonwoven materials are well known in the textile art, attempts to broadly apply such knowledge to produce products in the area of personal hygiene, such as catamenial devices, disposable diapers, incontinence pads and the like, have met with serious technical problems.
In general, such products must have a fluid absorbent core, usually comprising one or more layers of absorbent material such as wood pulp, rayon, gauze, tissue and the like and, in some cases, synthetic hydrophilic material such as a hydrophilic polyurethane foam.
Such fluid absorbing core is most generally fabricated in the form of a thermally bonded pad, of wood pulp, fiber and conjugate fiber, having a rectangular or somewhat oval shape. To protect a wearer's clothing, and surrounding areas from stain or wetting by fluids already absorbed in such a core, a fluid-impervious barrier sheet is usually required. In general, the absorbent device is positioned against the body of the user with hydrophilic material facing and contacting the body and the fluid impervious barrier sheet positioned on the outside or opposite side.
A particularly troublesome technical problem arises when a high degree of hydrophobicity is desired in a nonwoven component produced substantially from conventionally bonded webs of hydrophobic fiber such as polyolefin-containing staple or spun-bonded webs.
In general, untreated hydrophobic fiber quickly becomes unworkable due to friction and accumulated static charge generated during conventional spinning, cutting and carding operations. For this reason, the art has long recognized and used a variety of topically applied antistatic agents which change fiber surface properties sufficiently to permit such conventional fiber processing. In effect, however, such treatment also produces fiber, web and nonwoven product which is substantially more hydrophilic than the untreated spun fiber.
Because of the nature of commercial high speed operations, and the somewhat unpredictable affinity of such agents to individual batches or bales of hydrophobic fiber, it becomes very difficult to maintain adequate control over bonding steps and over the wetting characteristics of the final nonwoven product.
It is an object of the present invention to prepare a hydrophobic polyolefin-containing spun fiber or filament for processing such as intermediate cutting and carding steps without unduly interfering with subsequent bonding steps or sacrificing needed hydrophobic characteristics in the nonwoven product.